Model 31-N Rev A Low Pressure Reducing Gas Regulator; 1-1/2" Body Size, #6 (0.375") Orifice; Stainless Steel Body And Lower Case, Carbon Steel Spring Chamber, Arrangement/Position 1, Internal Sensing Unless External Sensing Option Is Specified; S50N Trim: 316L Stainless Steel Internals, BUNA-N Seat And Diaphragm; NPT End Connections; 5.0-7.0" wc Range Spring; OPT-25S: Stainless Steel Rain-Proof Bug Vent (Includes OPT-25: 1/4" NPT Spring Chamber Vent Tap)